How do I find out wich IUSR_ has acessed a system file?

For instance, how can I build a log file of IUSR_ that have sucessfully used createobject() to the cdonts.dll in my system32 directory?

I tried the Server′s Object Auditing Policies, and it does seem to do this... but not quite as I need it to be done. I can′t edit the auditing settings every time a new user is added or removed, nor add a group and expect the event log to tell me who in the group raised de event.

Can you help me do this in code?
Aleks